A number of applications require the use of a plurality of rechargeable batteries bundled together in a pack to provide energy for a particular need. In electrically powered vehicles, for example, several battery modules (typically about 12 volts per module) are connected in series to form a high voltage (e.g., 300+volts) battery pack. Such a vehicle pack must not only be sturdy to resist damage on impact, but must be capable of readily accepting or dissipating heat. When such a battery pack is charged or discharged (i.e., receives or delivers electric power respectively) for example, heat is produced which, if uncontrolled, can have a significant impact on the life and performance of the pack as a whole as well as the individual battery modules that form the pack. Temperature stability of the battery modules, individually and as a group, within a defined operating range is essential in maximizing the performance and longevity of a battery pack, and accordingly battery pack thermal management is important to battery pack designers.
It is known to space the individual battery modules from each other and to flow a cooling/heating medium (e.g. air) therebetween to cool or heat the batteries as may be needed. Uncontrolled air flow, however, results in unbalanced air flow such that the air does not flow past each battery at the same rate or same temperature. As a result, significant temperature variances can occur from one battery module to the next which is detrimental to the battery pack's performance and longevity especially some battery modules are allowed to operate at excessive high temperatures. What constitutes "excessively high" will depend on the chemistry of the particular battery. An excessively high temperature for a Pb-acid battery for example is about 65.degree. C. For Pb-acid a desirable operating range is about 25.degree. C. to about 40.degree. C.